In communication networks, there may be a challenge to obtain good performance and capacity for a given communication protocol, its parameters and the physical environment in which the communication network is deployed.
For example, standards for wireless communication networks are commonly based on usage of orthogonal frequency division multiplexing (OFDM). One reason may be that OFDM allows for relatively low complex processing in case of high data rates and large bandwidth where the communication channel is frequency selective. OFDM also allows for a simple way to share the channel between different users, as represented by wireless devices (WDs), by simply allocating different sets of sub-carriers to different wireless devices (i.e., users). This principle is known as orthogonal frequency-division multiple access (OFDMA). The set of sub-carriers allocated to different wireless devices may either be localized, i.e., where the sub-carriers to one user are provided next to one another, or the set of sub-carriers may be distributed, i.e., where the sub-carriers are spread out and interlaced with sub-carriers carrying data to other wireless devices.
For practical reasons, localized sub-carriers may typically be used. In downlink transmission, i.e., from the wireless network node to the wireless devices, the allocation of sub-carriers may in principle be such that the wireless network node allocates a sub-carrier to the wireless device that has the most favorable channel conditions. Such schemes of allocating the sub-carriers are commonly known as frequency selective scheduling.
Although frequency selective scheduling may potentially give a performance gain, it requires that the wireless network node has knowledge of the channels to the different wireless devices. Such knowledge is typically obtained through channel sounding. Channel sounding may be achieved by measuring the channels between the wireless network node and the different wireless devices, and based on the obtained measurements, the wireless network node may decide how to allocate sub-carriers to different wireless devices.
When a data packet is successfully demodulated, the receiving wireless device may immediately send a positive acknowledgement (ACK) in the form of an ACK packet (or frame) to the wireless network node. If the wireless network node that sends the data packet does not receive the ACK frame, it assumes that the data packet was not correctly received and may decide to re-transmit the data packet to the wireless device. OFDMA may trigger multiple ACKs because of simultaneous transmission to different wireless devices.
One issue with the frequency selective scheduling is that it requires knowledge of the channels in order to determine which sub-carriers to be associated with which wireless devices, and that the time required to obtain knowledge of the channels reduces the gain that may be obtained during the actual data transmission. In particular, in cases when the channels are changing fast, the overhead associated with channel measurements become prohibitive. In addition, when the number of wireless devices is large, so that a large number of channels need to be estimated, frequency selective scheduling may not be a feasible alternative.
Hence, there is still a need for improved frequency selective scheduling of wireless devices in communication networks.